Similarly to the ring of death, they send the player to their last visited hub upon dying to Solak when carried in the inventory, bypassing Death's office and the need to reclaim any items. The player's familiar is also kept, and if it was a Beast of Burden, all items it carried are also kept. The mushroom provides 5 free deaths this way before vanishing.
When dying with a ring of death equipped, charges on the mushrooms won’t be lost.
They have an "eat" option, but they cannot be eaten, and selecting it causes the player to say "I don't think these are for eating, but I do know they will keep me safe for up to 5 deaths at Solak!"